The monster spawner spawns mobs in an 8*8*3 area around it when the player is within 16 blocks of the spawner, provided suitable spawning locations for the block's mob type can be found in the area. The block will attempt to spawn 4 mobs around it, then wait from 10 to 39.95 seconds before spawning again.

Monster spawners are transparent in their rendering only - unlike most other transparent blocks, they can have torches and redstone placed on them, conduct a redstone current, suffocate mobs, and more.

A monster spawner is only active when a player is within a radius of 16 blocks from the spawner. While the block is active, it will spawn mobs within an 8×8×3 block volume (8 wide, 8 long, and 3 high) centered on the center of the block, effectively meaning mobs can spawn in a 9×9 area, or 3.5 blocks from the spawner. Mobs can spawn anywhere in this range that is suitable, with mobs more likely to spawn closer to the spawner than farther away. A spawner of a mob that only spawns in dark conditions will not spawn mobs in any blocks where the light level is higher than 7.

While mobs are spawned at fractional x and z-coordinates (i.e. not aligned to blocks), they are spawned at an integer y-coordinate. Horizontally, a mob can spawn with its center point anywhere within the 8×8 range, but vertically, mobs will spawn with their legs at either the same layer as the spawner block, one block above it, or one block below it.

For some types of mobs to spawn in the outer planes of the spawning volume, some planes outside the volume may also need to be free of opaque blocks to conform with the mobs' height, width, or other rules governing their individual spawn volumes. For mobs that are two or more blocks tall such as zombies, skeletons, or blazes to spawn in the top y-layer, the layer above that must contain only air.

↑8×8×3 is the actual volume across which spawners spawn entities, but this volume only contains the entity's center. The failure rate assumes 8×8×4 because it is a popular misconception that 8×8×4 is the maximum efficiency volume of empty space for mob spawners - it actually depends on the size of the entities themselves. Note that 10×10×4 is guaranteed to accommodate all of the above mobs. Also note that this failure rate only accounts for failures due to attempting to spawn a mob at the edges of the spawn range, not other causes of failure such as mobs attempting to spawn intersecting the spawner block itself.

For all of the volumes listed in the table, the horizontal plane is centered on the center of the spawner block. While the spawning volume for pigs is 8.9×8.9×2.9, the requirement of grass blocks that are necessary for pigs to spawn will reduce the actual volume in which they successfully spawn, however other mobs can spawn in mid-air, ignoring general rules about spawning on solid ground.

The spawner does not have to be within 4 blocks of the correct biome for it to spawn mobs. As such, spawners can place mobs where they normally wouldn't generate. For example, a mooshroom spawner will operate in a plains biome as long as there are any mycelium blocks within the spawn area.

The block will attempt to spawn 4 mobs at randomly chosen points within the spawning area, then wait anywhere from 200 to 799 ticks (10 to 39.95 seconds) before spawning again. As it waits, the mob inside the block will spin faster and faster. Except for spawning on a solid block, all of the usual requirements for spawning must be met (not in a solid block, correct light level, etc.), so the spawner will often produce fewer than 4 mobs. When it does spawn, it will "poof", and more lightless flames will temporarily appear around the Spawn block. If the block fails to spawn any mobs because it did not pick any suitable locations, it will repeat this process every tick until it succeeds. Only when it manages to spawn at least one mob will it start waiting for the next cycle. If, at the time of spawning, 6 or more mobs of the spawner's type are present within a 9×9×9 area, centered on the spawner block, the spawner "poofs" without creating any mobs and then waits for the next cycle.

When mining near a monster spawner that has no valid places to spawn, sometimes a monster will spawn immediately after a block is mined.

SpawnPotentials: Optional. List of possible entities to spawn. If this tag does not exist, but SpawnData exists, Minecraft will generate it the next time the spawner tries to spawn an entity. The generated list will contain a single entry derived from the EntityId and SpawnData tags.

: A potential future spawn. After the spawner makes an attempt at spawning, it will choose one of these entries at random and use it to prepare for the next spawn.

Entity: An entity. Overwrites SpawnData when preparing the next spawn, including the entity id.

Weight: The chance that this spawn will be picked as compared to other spawn weights. Must be non-negative and at least 1.

EntityIddeprecated in 1.9: The Entity ID of the next entity(s) to spawn. Both mob entity IDs and other entity IDs will work. Warning: If SpawnPotentials exists, this tag will get overwritten after the next spawning attempt: see above for more details. Use the "id" tag inside SpawnData (see below).

SpawnData: Contains tags to copy to the next spawned entity(s) after spawning. Any of the entity or mob tags may be used. Note that if a spawner specifies any of these tags, almost all variable data such as mob equipment, villager profession, sheep wool color, etc., will not be automatically generated, and must also be manually specified (note that this does not apply to position data, which will be randomized as normal unless Pos is specified. Similarly, unless Size and Health are specified for a Slime or Magma Cube, these will still be randomized). This, together with EntityId, also determines the appearance of the miniature entity spinning in the spawner cage. Note: this tag is optional: if it does not exist, the next spawned entity will use the default vanilla spawning properties for this mob, including potentially randomized armor (this is true even if SpawnPotentials does exist). Warning: If SpawnPotentials exists, this tag will get overwritten after the next spawning attempt: see above for more details.

SpawnCount: How many mobs to attempt to spawn each time. Note: Requires the MinSpawnDelay property to also be set.

SpawnRange: The radius around which the spawner attempts to place mobs randomly. The spawn area is square, includes the block the spawner is in, and is centered around the spawner's x,z coordinates - not the spawner itself. It is 2 blocks high, centered around the spawner's y coordinate (its bottom), allowing mobs to spawn as high as its top surface and as low as 1 block below its bottom surface. Vertical spawn coordinates are integers, while horizontal coordinates are floating point and weighted towards values near the spawner itself. Default value is 4.

Delay: Ticks until next spawn. If 0, it will spawn immediately when a player enters its range. If set to -1 (this state never occurs in a natural spawner; it seems to be a feature accessed only via NBT editing), the spawner will reset its Delay, and (if SpawnPotentials exist) EntityID and SpawnData as though it had just completed a successful spawn cycle, immediately when a player enters its range. Note that setting Delay to -1 can be useful if you want the game to properly randomize the spawner's Delay, EntityID, and SpawnData, rather than starting with pre-defined values.

MinSpawnDelay: The minimum random delay for the next spawn delay. May be equal to MaxSpawnDelay.

MaxSpawnDelay: The maximum random delay for the next spawn delay. Warning: Setting this value to 0 crashes Minecraft. Set to at least 1. Note: Requires the MinSpawnDelay property to also be set.

MaxNearbyEntities: Overrides the maximum number of nearby (within a box of spawnrange*2+1 x spawnrange*2+1 x 8 centered around the spawner block) entities whose IDs match this spawner's entity ID. Note that this is relative to a mob's hitbox, not their physical position. Also note that all entities within all chunk sections (16x16x16 cubes) overlapped by this box are tested for their ID and hitbox overlap, rather than just entities which are within the box, meaning a large amount of entities outside the box (or within it, of course) can cause substantial lag.

RequiredPlayerRange: Overrides the block radius of the sphere of activation by players for this spawner. Note that for every gametick, a spawner will check all players in the current world to test whether a player is within this sphere. Note: Requires the MaxNearbyEntities property to also be set.

Although in Bedrock Edition a spawner emits light level 3, the only effect on gameplay is to make an inactive spawner slightly more visible in a very dark area because mob spawning and crop growth effects are always the same for light levels 0-3.

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